ok, so if a lake on RE and a lake on FE both froze over they would both be flat. One would be Flat Flat and one would be Flat relative to the curve. So take a large block of ice and see if it is flat or curved. If it's flat, so is the world.
I'm trying to do my best to get my head into the FE model (which i like very much but an new to), It makes more sense to me for the world to be flat but all my "education" thus far has been RE so you have to forgive the odd hiccup in logic.